A conventional computer mainly uses an extractor fan located on its power supply for heat-radiation. The extractor fan starts to suck exterior air to the inside of the computer via a preset through hole on the computer. The air sucked in passes motherboard, hard disk, floppy disk, CPU, CD-ROM drive and so on, enters the power supply, and then is discharged out by the extractor fan. Although heat-radiating effect is accomplished, dust mites in air are also sucked into the computer and stay on various kinds of electronic components and the circuit. After accumulation for a long time, the heat-radiating effect of the circuit will be affected, and current leakage between electrodes of the circuit may easily arise due to humidity in air, hence letting the computer easily crash during operation at a high speed. More particularly, because the operation speed of a CPU becomes faster, the demand for heat-radiating effect is higher. The way of only using an extractor fan on the power supply for heat radiation cannot meet today's requirements. Accordingly, the above extractor fan of the conventional computer has inconvenience and drawbacks in practical use. The present invention aims to resolve the problems in the prior art.